At present, a difficulty of the co-frequency full-duplex technology is how to eliminate self-interference. Methods for interference elimination mainly include antenna interference elimination, radio frequency interference elimination, and digital interference elimination. The antenna interference elimination is used at an antenna end, and is passive interference elimination.
To realize the antenna interference elimination, the relevant technology proposes a solution, and in the solution, by controlling spatial positions of a receiving antenna and two transmitting antennas, interference of signals of the two transmitting antennas is eliminated at the receiving antenna. In the solution, a transmission signal is divided into two signals, and the two signals are transmitted to the two transmitting antennas respectively. The receiving antenna is arranged between the two transmitting antennas, and a difference between a distance between the receiving antenna and one of the two transmitting antennas and a distance between the receiving antenna and the other of the two transmitting antennas is an odd number of times as much as one half of the wavelength. Specifically, as shown in FIG. 1, if the wavelength of the transmission signal is λ, the transmission signal is divided into two signals after travelling through a radio frequency channel, and the two signals are transmitted to the two transmitting antennas respectively (that is, the transmitting antenna 102 and the transmitting antenna 106). Wherein, the distance between the transmitting antenna 106 and the receiving antenna 104 is d+λ/2, the distance between the transmitting antenna 102 and the receiving antenna 104 is d, and one of the two transmission signals is superimposed on the other of the two transmission signals at the receiving antenna 104. As a phase difference of the two transmission signals is π due to a path difference of a half of the wavelength, the interference of the superimposed transmission signals can be eliminated, and the strength of self-interference signals can be greatly reduced. Furthermore, when the strength of one of the two transmission signals is much closer to that of the other of the two transmission signals at the receiving antenna, the effect of interference elimination is much better, and the strength of interference of residual signals is much weaker.
In the above technical solution, two transmitting antennas and one receiving antenna are needed. The full-duplex communication mode can be realized, and to a certain degree, the throughput capacity of the system is also increased. However, the transmission signal is divided into two signals and the two signals are transmitted to different antenna channels, as it cannot guarantee that the characteristics of the two transmitting antennas are the same, even if the transmission signals respectively transmitted to the two transmitting antennas are the same, there are also different distortion and loss. Furthermore, the difference between the two signals is random, the greater the difference is, the poor the effect of interference elimination is, and the greater the strength of interference of the residual signals is.
Therefore, under the condition of not adding an active device, how to realize self-interference elimination of antennas, and also how to avoid a poor effect of interference elimination due to the fact that there are random errors in signals transmitted by two transmitting antennas, have become technical problems which are needed to be instantly solved.